1. Field of the Invention
This invention relates to an image vibration correcting device used in an image pickup apparatus such as a television camera or a video camera and capable of obtaining a stable image free of image vibration when disturbance vibration is applied to the image pickup apparatus.
2. Related Background Art
In recent years, image pickup apparatus such as television cameras and video cameras have been advanced in their automatization and the technique of realizing the vibration correcting function of automatically correcting image vibration attributable to the vibration of the entire apparatus has also been put into practical use.
As vibration correcting means, there is known a variable angle prism which, as shown in FIG. 11 of the accompanying drawings, is disposed on the photo-taking optical path of a photo-taking lens and inclines the photo-taking optical path by the relative tilting of a pair of transparent plates having transparent liquid interposed therebetween to thereby correct the vibration of an image field.
That is, two transparent plates 1 and 2 each comprising a glass plate or the like have their outer peripheral frame members 3 and 4 sealed by bellows-like film 5, and this hermetically sealed space is filled with liquid of a high refractive index, and a variable angle prism 6 is constituted by these.
The frame member 3 has a flattened coil 7 secured to one end thereof, and permanent magnets 8 and yokes 9, 10 opposed to each other with the coil 7 interposed therebetween are disposed on the opposite sides of the coil 7 to thereby constitute driving means 11 comprising a closed magnetic circuit. The frame member 3 also is provided with an arm 13 having a slit 12, and a light emitting element 14 and a light receiving element 15 are disposed on the opposite sides of the arm 13 in an opposed relationship with each other, and a beam of light emitted from the light emitting element 14 may pass through the slit 12, and thereafter may be applied to the light receiving element 15. The light emitting element 14 is, for example, an infrared light emitting element emitting infrared light such as an IRED, and the light receiving element 15 is, for example, a photoelectric conversion element such as a PSD of which the output is varied by the spot position of the received beam of light.
The frame member 4 is also provided with an arm 17 having a slit 16, and, although not shown, there are disposed a flattened coil, permanent magnets, yokes, a light emitting element and a light receiving element similar to those on the frame member 3 side.
On the supporting portion of the apparatus, vibration detectors 18 and 19 as vibration detecting means are mounted with respect to the pitch direction P and the yaw direction Y so as to be capable of detecting the amounts of vibration of the entire apparatus in the pitch direction P and the yaw direction Y, and there are provided a control circuit 20 as control means comprised of an A/D converter, a D/A converter, a CPU, a memory, etc. and receiving as inputs the detection signals of the vibration detectors 18 and 19 and controlling a system, and a coil driving circuit 21 for supplying an electric current to the coil 7 on the frame member 3 side and the coil on the frame member 4 side in accordance with the command of the control circuit 20.
The frame members 3 and 4 are supported on a frame, not shown, by a pitch shaft P and a yaw shaft Y, and a lock pin 24 protruding to the outside in the direction of the pitch shaft P is secured to the outer peripheral surface of the frame member 4. A lock knob 25 formed with a V-shaped recess for receiving the lock pin 24 is provided on the frame and also, a limit switch 26 for detecting the operated position of the lock knob 25 is provided. Although not shown, a lock pin 24, a lock knob 25 and a limit switch 26 are also disposed on the frame member 3 centering around the direction of the yaw shaft Y to lock the frame member 3 in its neutral position.
In an operator's the image vibration preventing device of such a construction, when vibration is caused to the entire apparatus due to the vibration of the hands holding the entire apparatus, disturbance vibration or the like, the vibration detectors 18 and 19 detect the vibration and the signals thereof are inputted to the control circuit 20, whereby the vertical angle of the variable angle prism 6 necessary to eliminate the vibration is calculated.
On the other hand, the fluctuation of the angles of rotation of the opposed transparent plates 1 and 2 about the shafts P and Y, i.e., the vertical angles of the variable angle prism 6 in the pitch and yaw directions, causes a fluctuation to the spot position on the light receiving surface when the beam of light emitted from the light emitting element 14 is transmitted through the slits 12 and 16 formed in the arms 14 and 17 of the frame members 3 and 4 rotated with the opposed transparent plates 1 and 2 and enters the light receiving element 15. The light receiving element 15 transmits to the control circuit 20 an output conforming to the amount of movement of the spot thereon, i.e., the magnitude of the vertical angle of the variable angle prism 6. This control circuit 20 calculates the difference between the magnitude of the aforementioned calculated vertical angle and the magnitude of the vertical angle at the present point of time and transmits it to the coil driving circuit 21. This coil driving circuit 21 supplies the coil 8 with a driving current conforming to a coil driving command signal.
The variable angle prism 6 effects rotative movement about the shafts X and Y by the coil 8 and is deformed so as to coincide with the magnitude of the aforementioned calculated vertical angle. That is, the variable angle prism 6 is designed to effect the correction control of vibration by feedback control using the value of the vertical angle calculated so as to correct vibration as a reference signal and using the value of the current vertical angle as a feedback signal.
Also, when vibration correction is not effected, the lock knob 25 is moved upwardly and the lock pin 24 is held in the recess at the upper end of the lock knob 25. Thereupon, the frame member 4 becomes unable to rotate relative to the yaw shaft Y and is locked in the yaw direction. On the other hand, when the lock knob 25 is moved up to its lock position, the limit switch 26 is operated and the operation is transmitted to the coil driving circuit 21 and in conformity therewith, the supply of electric power to the coil of the frame member 4 is stopped. Although not shown in FIG. 11, the pitch direction P is likewise locked. Besides this, there is a system which, when the operation of the camera is in a standby state, electrically moves the lock knob 25 up to its lock position in response to this state and stops vibration correction.
However, for the above-described example of the conventional art to be used in the large photo-taking lens, particularly the high-magnification photo-taking lens, of a television camera or the like, the variable angle prism 6 generally disposed forwardly of the front lens portion of the high-magnification photo-taking lens need be made large when the effective beam of light of the lens is taken into consideration. Accordingly, the driving means for tilting the transparent plates 1 and 2 of the variable angle prism 6 also becomes bulky and the image vibration correcting device tends to become bulky. Further, the balkiness of the device including the photo-taking lens and an increase in the weight thereof result.
Therefore, there is not so great a problem in the photographing on a vehicle or a helicopter, while during the photographing on a shoulder, i.e., the photographing in hands, there is the disadvantage that the mobility thereof is lost.